Thermally stable fuel compositions



United States Patent 3,416,903 THERMALLY STABLE FUEL COMPOSITIONS George W. Eckert and Doris Love, Wappingers Falls, N.Y., assignors to Texaco Inc., New York, N.Y., a corporation of Delaware No Drawing. Filed Dec. 26, 1967, Ser. No. 693,141 6 Claims. (CI. 44-73) ABSTRACT OF THE DISCLOSURE Thermally stable middle distillate or jet fuel composition containing a Mannich base from an alkylphenol sulfide, formaldehyde and alkylene diamine.

This invention relates to mineral oil compositions and, more particularly, to petroleum hydrocarbon middle distillate and jet fuel compositions having improved thermal stability.

It is recognized that petroleum hydrocarbon middle distillates and jet fuels are susceptible to oxidation resulting in the formation of a suspension of finely divided insoluble bodies in the fuel and the formation of deposits. The degree to which these undesirable changes take place is dependent on the amount of the unstable constituents present in the oil and on the temperature and oxidation conditions to which the oil is subjected. The ratings of the changes by the CFR Fuel Coker Test are accepted standards of the thermal stability of the fuel tested.

The problem of thermal stability is particularly serious for hydrocarbon oils which must be maintained at a relatively high temperature for extended periods of time in intimate contact with oxygen or in an oxygen-containing atmosphere. Such is the situation in regard to light middle distillates and jet fuel compositions which are maintained at elevated temperatures of several hundred degrees for many hours while being constantly agitated in contact With air. This problem becomes acute for jet fuel compositions designed to fuel aircraft having speeds in the Mach 2 speed range or above such as the forthcoming supersonic transports because of the substantially higher skin and wing tank temperatures generated.

When a middle distillate or jet fuel has insufficient thermal stability, degradation results in the formation of a suspension of finely divided insoluble bodies. These insoluble bodies are separated from the fuel in the fuel filters of the engine. When there is an excessive amount of insoluble bodies present in the fuel, the fuel line filters become partially or completely blocked resulting in seriously curtailed or lost engine power due to fuel starvation.

Deposit formation which also occurs in a thermally unstable fuel causes a deposit build-up referred to as heater tube deposits in various parts of the engine. Excessive heater tube deposits can become critical and lead to loss of power or even engine malfunction with serious consequences resulting therefrom. Both of these fuel properties are measured in the above-noted CPR Fuel Coker Test.

A middle distillate fuel oil composition has now been discovered having improved thermal stability. More particularly, a jet fuel composition has been discovered which exhibits outstanding thermal stability for long periods of time while being maintained at a high temperature under constant agitation in the presence of air.

In accordance with this invention, there is provided a middle distillate fuel composition of enhanced thermal stability containing a minor amount of a Mannich base. More particularly, a middle distillate fuel or jet fuel corri position is provided containing from about 0.001 to 0.50 Weight percent of a Mannich base reaction product formed 3,416,903 Patented Dec. 17, 1968 from an alkylphenol sulfide, formaldehyde and an alkylene diamine. More particularly, an alkylphenol sulfide, defined below, formaldehyde and an alkylene di-amine, defined below, may be reacted in mole ratios of azbzl respectively where a and b each can have a value from 1 to 8 but a is never greater than b or greater than x+4 to form the thermal stability additive of the invention.

The alkylphenol sulfide component of the reaction product is represented by the formula:

in which R is an alkyl radical having from 4 to 60 carbon atoms and z is 1 or 0. The preferred alkylphenol sulfides are those in which R is an alkyl radical having from 10 to 18 carbon atoms and z has a value of one. When 2 is 0, the alkylphenol sulfide contains 2 moles of an alkylphenol and 1 mole of sulfur (2:1) and when z is l the alkylphenol sulfide contains three moles of an alkylphenol and 2 moles of sulfur (3 :2). Alkylphenol sulfides are prepared by reacting suitable proportions of an alkylphenol With sulfur dichloride. These materials are reacted in a solvent, such as isooctane, at a moderate temperature generally from about 15 to 25 C. The reaction mixture is heated to reflux temperature to effect solvent removal and recovery of the alkylphenol sulfide.

The alkylene diamine component of the reaction product is represented by the formula:

in which x has a value of 0 to 4. The preferred alkylene diamine for the reaction product is ethylenediamine.

The alkylphenol sulfide, formaldehyde and alkylene diamine components of the reaction product may be reacted in mole ratios of azbzl respectively where a and b each can have a value from 1 to 8 but ais never greater than b or greater than x+4. In general, preparation of the reaction product involves mixing the alkylphenol sulfide with alkylene diamine and then adding the formaldehyde solution. The reactants are heated with stirring to a temperature of about 80 C. (176 F.) to effect the reaction. Water is then stripped out of the reaction mixture and the temperature raised to about 143 C. (290 F.) to insure completion of the reaction. Upon completion of the reaction, a hydrocarbon oil is added to the reaction mixture to make an oil blend of the reaction product. This blend is filtered to remove any insoluble materials.

A 50% concentration of the active additive reaction product in the oil blend is very convenient for subsequent addition to a fuel composition.

Preparation of the fuel composition of the invention sirnply involves the addition of a suitable amount of the Mannich base-oil blend to the base fuel followed by mixing to effect complete dispersion of the additive in the fuel. In general, the fuel composition of the invention will contain from about 0.001 to 0.50 weight percent of the Mannich base calculated on an active material (Mannich base) basis. The preferred concentration of the additive in the fuel ranges from about .003 to .006 weight percent which amounts correspond to about 8 and 16 lbs. of additive per thousand barrels of fuel.

The thermal stability additive of the invention is effective in middle distillates and jet fuels boiling in the range from about to 600 F.

The following examples illustrate the preparation of the additive of the invention.

3 EXAMPLE 1 618 grams (6.0 moles) of sulfur dichloride was added to a mixture of 3660 grams (12.0 moles) of tetrapropenyl phenol and about 2000 ml. of isooctane while the mixture was maintained at a temperature ranging from to C. The reaction mixture was maintained in this temperature range for about 60 minutes after which the solution was heated to reflux and the isooctane distilled off to effect recovery of the tetrapropenyl phenol sulfide.

40.5 grams (0.50 mole) of 37 (w.) percent aqueous formaldehyde was added to a mixture of 16.5 grams (0.25 mole) of 85 (-W.) percent aqueous ethylenediamine and 321 grams (0.50 mole) of tetrapropenyl phenol sulfide. The mixture was then heated to 80 C. (175 F.) and stirred there for 6 hours. The water was then stripped off and the temperature of the reaction mixture raised to about 143 C. (290 F.) to complete the formation of the reaction product. The reaction product was taken up in approximately 343 grams of oil to form about a by weight blend of the tetrapropenylphenol sulfide- 4 12.0 inches of mercury in 300 minutes is satisfactory (see MILJ-5624F)'.

The base fuel employed in these tests was a typical jet fuel having the following properties:

The effectiveness of the additives of the invention in the above jet fuel is shown by the CFR Fuel Coker Test results set forth in Table 1 below:

TABLE I.THERMAL STABILITY ITIYEESS F RESULTS BY CFR FUEL COKER Concentra- Pressure Additive in base fuel tion of Tube additive rating Inches, Time, PTB lig. min.

1 Base fuel (no additive) 4 25.0 104 2 tive 16 2 0.0 300 3 16 2 0. 0 300 4 o 8 1 0 0 300 5 Tetrapropenylphenol sulfide (2:1): formaldehyde: di-

methylamine (1:2:2 mole ratio) 16 4 6 Tetrapropenylphenol: formaldehyde: ethylenediamine (1: 1.6:0.67 mole ratio) 16 4 T Tetrapropenylphenol: formaldehyde: tetraethylene pentamine (2:2:1 mole ratio) .l I 16 4 25 300 formaldehyde-ethylene diamine reaction product in oil. The reaction product (active material) of this example was called Additive A.

EXAMPLE 2 3660 grams (12.0 moles) of tetrapropenyl phenol and 824 grams (80 moles) of sulfur dichloride were reacted in isooctane as in Example 1 to form a tetrapropenylphenol sulfide in the mole proportions of 3 moles of alkylphenol and 2 moles sulfur.

328 grams (0.34 mole) of the above tetrapropenylphenol sulfide, grams (0.68 mole) 37 (w.) percent aqueous formaldehyde and 22.4 grams (0.34 mole) 85 (w.) percent aqueous ethylenediamine were reacted as in Example 1. Approximately equal weight amount of oil was added to the reaction product to form approximately 21 50 percent by weight blend of the active material in the oil solution. The reaction product (active material) of this example was called Additive B.

The effectiveness of the additives of the invention for improving the thermal stability of a fuel was determined by adding a small amount of additive to a typical jet fuel composition and testing for thermal stability properties in the CFR Fuel Coker Test. The CFR Fuel Coker Test is described in ASTMD1660-61T Thermal Stability of Aviation Turbine Fuels, and this test measures both tube deposits (tube rating) and filter plugging caused by the fuels. The conditions under which this test was conducted are as follows: The preheater temperature employed was 450 F. and the filter temperature was 550 F. The fuel flow was at a rate of 6 lbs. per hour for 5 hours (300 minutes). If the back pressure caused by filter plugging reaches 25.0 inches of mercury before the 300 minutes, the run is stopped and the pressure and time are recorded. The deposits formed on the tube are rated as 0, 1, 2, 3, or 4 (where 0=best; 4=worst) depending on the extent of the deposit formation on the tube.

Under the specified conditions, a tube rating of 2 or less is satisfactory, and a filter pressure of less than The foregoing results in Runs 2, 3 and 4 show the outstanding effectiveness of the thermal stability additives of the invention. In contrast, similar Mannich bases shown in Runs 5, 6 and 7 were totally ineffective in the tube rating and Run 7 was also ineffective on the filter plugging basis.

Obviously, many modifications and variations of the invention, as hereinafter set forth, may be made without departing from the spirit and scope thereof, and therefore, only such limitations should be imposed as are indicated in the appended claims.

We claim:

1. A middle distillate fuel composition consisting of petroleum hydrocarbons boiling in the range from about to 600 F. containing from about .001 to 0.50 weight percent of the reaction product of an alkylphenol sulfide, formaldehyde and an alkylene diamine in mole proportions of azbzl respectively, where a and b each can have a value from 1 to 8 but a is never greater than b or greater than x| 4, said alkylphenol sulfide having the formula ([31]: r (|)II 1 911 s Q O R R z R in which R is an alkyl radical having from 4 to 60 carbon atoms and z is 1 or 0, and said alkylene diamine has the formula in which x has the value of 0 to 4.

2. A middle distillate f-uel composition according to claim 1 in which the alkyl radical R in said alkylphenol sulfide has from 10 to 18 carbon atoms.

3. A middle distillate fuel composition according to claim 1 in which said alkylphenol sulfide is tetrapropenylphenol sulfide (3:2 mole ratio) and said alkylene diamine is ethylenediamine.

4. A middle distillate fuel composition according to claim 1 in which said alkylphenol sulfide is tetrapropenylphenol sulfide (2:1 mole ratio) and said alkylene diamine is ethylenediamine.

5. A middle distillate fuel composition according to claim 1 in which a and b each have the value of 2.

6. A middle distillate fuel composition according to UNITED STATES V PATENTS 2,962,442 11/1960 Andress 44-73 XR 2,984,550 5/1961 Chamot 44.73 XR DANIEL E. WYMAN, Primary Examiner.

10 W. J. SHINE, Assistant Examiner. 

